With eyeglass clips which are attached by means of conventional attachments, the clips may become disengaged by torsion. As the frame is twisted or turned in any axial, radial or other direction, the clips will become dislodged from the primary frame, thus falling off or, at a minimum, becoming out of alignment and perhaps partially disconnected from the primary frame. To address this problem the rigidity of the primary frame must therefore be balanced, so as not to deform too much when subjected to various types of torsion. This has been true of primary frames used in association with both of magnetic and non-magnetic auxiliary frames. Today, frames are commonly manufactured with more flexible materials.
Another alternative has been to have an auxiliary eyeglass frame made out of extremely flexible material. However, auxiliary frame of this type have the disadvantage of being very fragile.
Various types of auxiliary eyeglass frames which contain magnetic material to facilitate adhesion to the primary eyeglass frame have been disclosed in the prior art. U.S. Pat. No. 4,070,103 discloses an eyeglass frame in which the peripheral edges of the primary frame and lens rim covers contain magnetic strips to hold the lens rim cover in place on the primary frame. U.S. Pat. No. 5,416,537 discloses an eyeglass frame which contains magnetic members on the temple of the primary frame which engage a corresponding magnetic member on the temple of the auxiliary frame. U.S. Pat. No. 5,642,177 discloses an auxiliary eyeglass frame which uses the same principle of magnets on the temporal portions as U.S. Pat. No. 5,416,537; however the auxiliary frame disclosed in U.S. Pat. No. 5,642,177 contains a hinge on the bridge of the frame which allows it to be folded. U.S. Pat. No. 5,568,207 discloses an auxiliary frame which contains small extensions on the temporal portions of the frame which secure the auxiliary frame to the primary eyeglass frame in addition to using the principle of magnetic members as disclosed in U.S. Pat. Nos. 5,416,537, 6,012,811 discloses an auxiliary eyeglass frame in which the bridge includes a U-shaped structure having two arms on the top and bottom of the bridge, respectively, with magnets located in respective arms, and the bridge of the primary frame, including its magnetic member, is sandwiched between the two arms.
There are many disadvantages to the eyeglasses described above. The auxiliary eyeglass frame described in U.S. Pat. No. 4,070,103 requires magnetic strips on both the primary and auxiliary frames. The auxiliary eyeglass frame described in U.S. Pat. No. 5,416,537 has the magnets attaching at the top of the primary frame, thus requiring the wearer to be extraordinarily precise in placing the auxiliary frame on the primary frame. The auxiliary eyeglass frame disclosed in U.S. Pat. No. 5,642,177 has front mounted magnets, which may cause the auxiliary frame to separate from the primary frame if jostled by the wearer.
Canadian patent 2,235,798, Canadian application 2,258,142, and U.S. Pat. No. 5,894,335 provide other examples of mechanical and/or magnetic attachment of auxiliary and primary frames.